In internal combustion engines the intake and exhaust valves are actuated by cams, which are designed to lift the valves at precisely the correct instant of piston travel and hold them open long enough to attain the most efficient filling and emptying of the cylinder. In many engine designs the cam activates a pushrod which, in turn, activates a rocker arm which pushes against the end of the valve stem thereby opening the valve. The pushrod, rocker arm, and valve are the primary components of the engine valve train in such engine designs.
A long standing goal of engine design is to produce greater engine power while simultaneously achieving better fuel economy. Engine components of a lighter weight further this goal because lower engine component weight decreases the amount of work necessary for operation, thereby increasing engine efficiency. Heavier valve train components, on the other hand, require more power to move, which reduces the amount of power which the engine is capable of producing and causes more wear on the engine. The mass of the valve train components is also a factor limiting the maximum RPM capability of the engine. Heavier valve trains also require higher valve spring pressures which are needed to hold the valve train in engagement with the cam to follow the cam profile. This higher spring pressure also causes additional wear.
Many engines require, by design, relatively long pushrods. The stresses generated by these engines can cause the rods to flex or bend. This pushrod flex can alter the designed performance of the engine by reducing valve lift and changing the valve timing. Pushrod flex also causes excessive clearance between the pushrod and adjacent engine parts, resulting in high stress and undue wear to the entire valve train. In extreme cases of excessive clearance a pushrod may become disengaged completely, causing severe damage to the engine.
What is desired, therefore, is a pushrod which is both lightweight and capable of maintaining rigidity under the high stresses generated by an engine in order to maintain designed valve operation.